Leukotrienes are lipid-derived cell mediators that are released in response to a variety of immunologic and inflammatory stimuli. They are products of arachidonic acid metabolism derived through the 5-lipoxygenase pathway. Briefly, the initial step in leukotriene production involves oxygenation of arachidonic acid to produce 5S-hydroperoxy-6,8-trans-11,14 cis-eicosatetraenoic acid (5-HPETE), a subsequent dehydrase step producing the epoxide intermediate, 5,6-trans-oxido-7,9-trans-11,14-cis-eicosatetraenoic acid (LTA.sub.4). Two routes of metabolism from LTA.sub.4 lead to the production of biologically active products. One of these pathways involves conjugation of LTA.sub.4 with glutathione (GSH) via LTC.sub.4 synthase to produce the sulfur-containing leukotriene 5S-hydroxy-6R-S-glutathionyl-7,9-trans-11,14 cis-eicosatetraenoic acid (LTC.sub.4). It is generally believed that LTC.sub.4 synthase is a member of the glutathione-S transferase enzyme family.
LTC.sub.4 has been implicated in a wide variety of diseases and pathologic conditions. LTC.sub.4 has been identified in fluids from psoriatic lesions and bronchial secretions associated with adult respiratory distress syndrome and neonatal pulmonary hypertension. For review, see Lewis et al., New England J. Med., 323: 645 (1990), incorporated herein by reference.
Although the other enzymatic members of the 5-lipoxygenase pathway have been cloned, the cloning of LTC.sub.4 synthase has been problematic. This is partly because the synthase is very labile in partially purified form and because the endogenous production of LTC.sub.4 synthase in normal human cells is extremely small. LTC.sub.4 synthase is present only in limited types of normal human cells, namely granulocytes derived from bone marrow. Moreover, oligonucleotides developed from the N-terminal region of the LTC.sub.4 synthase polypeptide have not been specific enough to develop an effective screen because the N-terminal region is highly degenerate. In addition, an effective immunoassay for LTC.sub.4 which relies on incubation of substrate has also been problematic since breakdown products of the substrate have been shown to cross-react with antibodies used in the assay.
It has already been established that inhibitors of 5-lipoxygenase and of the cell receptors for leukotrienes are of substantial efficacy in the management of patients with bronchial asthma. Given that that are only three points at which the leukotriene metabolic system can be disrupted: the activation and function of 5-lipoxygenase; the receptor for the leukotriene; or the function of LTC.sub.4 synthase; characterization of LTC.sub.4 synthase would be important, notwithstanding the problems associated with its cloning.